SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  fv.position, 
  fvd.variant 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_feature_variants AS fv ON pfv.feature_id = fv.feature_id 
  AND pfv.variant_id = fv.variant_id 
  INNER JOIN cscart_product_feature_variant_descriptions AS fvd ON pfv.variant_id = fvd.variant_id 
  AND fvd.lang_code = 'en' 
WHERE 
  pfv.feature_id IN (67, 103, 65, 63, 74, 102) 
  AND pfv.product_id IN (
    65146, 65190, 65192, 65163, 65184, 65178, 
    65175, 65177
  ) 
  AND pfv.lang_code = 'en'

Query time 0.00355

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "54.52"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "variant_id",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id",
            "fl"
          ],
          "key": "idx_product_feature_variant_id",
          "used_key_parts": [
            "product_id",
            "feature_id",
            "lang_code"
          ],
          "key_length": "12",
          "rows_examined_per_scan": 48,
          "rows_produced_per_join": 48,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "5.50",
            "eval_cost": "4.80",
            "prefix_cost": "10.30",
            "data_read_per_join": "1K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ],
          "attached_condition": "((`cscart_db`.`pfv`.`feature_id` in (67,103,65,63,74,102)) and (`cscart_db`.`pfv`.`product_id` in (65146,65190,65192,65163,65184,65178,65175,65177)) and (`cscart_db`.`pfv`.`lang_code` = 'en'))"
        }
      },
      {
        "table": {
          "table_name": "fv",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "feature_id",
            "variant_feature_idx",
            "idx_var_feat_pos"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "cscart_db.pfv.variant_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 32,
          "filtered": "67.20",
          "cost_info": {
            "read_cost": "20.57",
            "eval_cost": "3.23",
            "prefix_cost": "35.67",
            "data_read_per_join": "36K"
          },
          "used_columns": [
            "variant_id",
            "feature_id",
            "position"
          ],
          "attached_condition": "(`cscart_db`.`fv`.`feature_id` = `cscart_db`.`pfv`.`feature_id`)"
        }
      },
      {
        "table": {
          "table_name": "fvd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "cscart_db.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 32,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "15.62",
            "eval_cost": "3.23",
            "prefix_cost": "54.52",
            "data_read_per_join": "241K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}